The present invention relates to a photocatalyst, a process for the photocatalyst and a photocatalyst coating composition comprising the photocatalyst.
Ultraviolet irradiation to a semiconductor generates electrons having a strong reduction activity and positive holes having a strong oxidation activity, so as to decompose a molecular species that comes in contact with the semiconductor by the oxidation-reduction activity. Such an activity is called a photocatalytic activity. By the photocatalytic activity, substances such as organic solvents are decomposed and removed. As a substance showing the photocatalytic activity, titanium oxide is attracting much attention and photocatalysts made of titanium oxide are in the market.
However, when the photocatalysts made of titanium oxide available in the present market are irradiated with visible light, the photocatalysts only shows insufficient photocatalytic activity.
The objects of the present invention are to provide a photocatalyst that shows sufficiently high photocatalytic activities by irradiation of visible light, to provide a process for producing the photocatalyst and to provide a photocatalyst coating composition comprising the photocatalyst titanium oxide.
The present inventors have studied on titanium oxide and other compounds in order to achieve such objects. As a result, the present inventors have found that the objects and other objects are achieved by a photocatalyst comprising a titanium oxide and a metal-containing compound other than titanium oxide on the surface of the titanium oxide, and have completed the present invention.
Thus, the present invention provides a photocatalyst comprising a titanium oxide and a metal-containing compound other than titanium oxide on the surface of the titanium oxide, wherein the metal-containing compound is a metal oxide having an acid site and the photocatalyst has a BET specific surface area of about 55 m2/g or larger, or wherein the metal-containing compound is a basic metal-containing compound and the photocatalyst has an anatase-crystalline structure and an anatase-crystalline size of about 10 nm or larger.
The present invention also provides a process for producing the above-described photocatalyst, for example, which comprises the steps of allowing a titanium oxide to come in contact with a solution or slurry of a metal-containing compound other than titanium oxide and/or a solution or slurry of a compound which makes the metal-containing compound by heating; and heating the resulting titanium oxide to obtain a photocatalyst.
The present invention further provides a photocatalyst coating composition comprising the above-described photocatalyst and a solvent.